Re: [Rd] Shouldn't vector indexing with negative out-of-range index give an error?
John Chambers j...@stat.stanford.edu
on Tue, 5 May 2015 08:39:46 -0700 writes:
When someone suggests that we might have had a reason for some
peculiarity in the original S, my usual reaction is Or else we never thought
of the problem.
In this case, however, there is a relevant statement in the 1988 blue
book. In the discussion of subscripting (p 358) the definition for negative i
says: the indices consist of the elements of seq(along=x) that do not match
any elements in -i.
Suggesting that no bounds checking on -i takes place.
John
Indeed!
Thanks a lot John, for the perspective and clarification!
I'm committing a patch to the documentation now.
Martin
On May 5, 2015, at 7:01 AM, Martin Maechler
maech...@lynne.stat.math.ethz.ch wrote:
Henrik Bengtsson henrik.bengts...@ucsf.edu
on Mon, 4 May 2015 12:20:44 -0700 writes:
In Section 'Indexing by vectors' of 'R Language Definition'
(http://cran.r-project.org/doc/manuals/r-release/R-lang.html#Indexing-by-vectors)
it says:
Integer. All elements of i must have the same sign. If they are
positive, the elements of x with those index numbers are selected. If
i contains negative elements, all elements except those indicated are
selected.
If i is positive and exceeds length(x) then the corresponding
selection is NA. A negative out of bounds value for i causes an error.
A special case is the zero index, which has null effects: x[0] is an
empty vector and otherwise including zeros among positive or negative
indices has the same effect as if they were omitted.
However, that A negative out of bounds value for i causes an error
in the second paragraph does not seem to apply. Instead, R silently
ignore negative indices that are out of range. For example:
x - 1:4
x[-9L]
[1] 1 2 3 4
x[-c(1:9)]
integer(0)
x[-c(3:9)]
[1] 1 2
y - as.list(1:4)
y[-c(1:9)]
list()
Is the observed non-error the correct behavior and therefore the
documentation is incorrect, or is it vice verse? (...or is it me
missing something)
I get the above on R devel, R 3.2.0, and as far back as R 2.11.0
(haven't check earlier versions).
Thank you, Henrik!
I've checked further back: The change happened between R 2.5.1 and R
2.6.0.
The previous behavior was
(1:3)[-(3:5)]
Error: subscript out of bounds
If you start reading NEWS.2, you see a *lot* of new features
(and bug fixes) in the 2.6.0 news, but from my browsing, none of
them mentioned the new behavior as feature.
Let's -- for a moment -- declare it a bug in the code, i.e., not
in the documentation:
- As 2.6.0 happened quite a while ago (Oct. 2007),
we could wonder how much R code will break if we fix the bug.
- Is the R package authors' community willing to do the necessary
cleanup in their packages ?
Now, after reading the source code for a while, and looking at
the changes, I've found the log entry
r42123 | ihaka | 2007-07-05 02:00:05 +0200 (Thu, 05 Jul 2007) | 4 lines
Changed the behaviour of out-of-bounds negative
subscripts to match that of S. Such values are
now ignored rather than tripping an error.
So, it was changed on purpose, by one of the true Rs, very
much on purpose.
Making it a *warning* instead of the original error
may have been both more cautious and more helpful for
detecting programming errors.
OTOH, John Chambers, the father of S and hence grandfather of R,
may have had good reasons why it seemed more logical to silently
ignore such out of bound negative indices:
One could argue that
x[-5] means leave away the 5-th element of x
and if there is no 5-th element of x, leaving it away should be a no-op.
After all this musing and history detection, my gut decision
would be to only change the documentation which Ross forgot to change.
But of course, it may be interesting to hear other programmeR's feedback
on this.
Martin
__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] Shouldn't vector indexing with negative out-of-range index give an error?
On Wed, May 6, 2015 at 1:33 AM, Martin Maechler
maech...@lynne.stat.math.ethz.ch wrote:
John Chambers j...@stat.stanford.edu
on Tue, 5 May 2015 08:39:46 -0700 writes:
When someone suggests that we might have had a reason for some
peculiarity in the original S, my usual reaction is Or else we never thought
of the problem.
In this case, however, there is a relevant statement in the 1988 blue
book. In the discussion of subscripting (p 358) the definition for negative
i says: the indices consist of the elements of seq(along=x) that do not
match any elements in -i.
Suggesting that no bounds checking on -i takes place.
John
Indeed!
Thanks a lot John, for the perspective and clarification!
I'm committing a patch to the documentation now.
Thank you both and also credits to Dongcan Jiang for pointing out to
me that errors were indeed not generated in this case.
I agree with the decision. It's interesting to notice that now the
only way an error is generated is when index-vector subsetting is done
using mixed positive and negative indices, e.g. x[c(-1,1)].
/Henrik
Martin
On May 5, 2015, at 7:01 AM, Martin Maechler
maech...@lynne.stat.math.ethz.ch wrote:
Henrik Bengtsson henrik.bengts...@ucsf.edu
on Mon, 4 May 2015 12:20:44 -0700 writes:
In Section 'Indexing by vectors' of 'R Language Definition'
(http://cran.r-project.org/doc/manuals/r-release/R-lang.html#Indexing-by-vectors)
it says:
Integer. All elements of i must have the same sign. If they are
positive, the elements of x with those index numbers are selected. If
i contains negative elements, all elements except those indicated are
selected.
If i is positive and exceeds length(x) then the corresponding
selection is NA. A negative out of bounds value for i causes an error.
A special case is the zero index, which has null effects: x[0] is an
empty vector and otherwise including zeros among positive or negative
indices has the same effect as if they were omitted.
However, that A negative out of bounds value for i causes an error
in the second paragraph does not seem to apply. Instead, R silently
ignore negative indices that are out of range. For example:
x - 1:4
x[-9L]
[1] 1 2 3 4
x[-c(1:9)]
integer(0)
x[-c(3:9)]
[1] 1 2
y - as.list(1:4)
y[-c(1:9)]
list()
Is the observed non-error the correct behavior and therefore the
documentation is incorrect, or is it vice verse? (...or is it me
missing something)
I get the above on R devel, R 3.2.0, and as far back as R 2.11.0
(haven't check earlier versions).
Thank you, Henrik!
I've checked further back: The change happened between R 2.5.1 and R
2.6.0.
The previous behavior was
(1:3)[-(3:5)]
Error: subscript out of bounds
If you start reading NEWS.2, you see a *lot* of new features
(and bug fixes) in the 2.6.0 news, but from my browsing, none of
them mentioned the new behavior as feature.
Let's -- for a moment -- declare it a bug in the code, i.e., not
in the documentation:
- As 2.6.0 happened quite a while ago (Oct. 2007),
we could wonder how much R code will break if we fix the bug.
- Is the R package authors' community willing to do the necessary
cleanup in their packages ?
Now, after reading the source code for a while, and looking at
the changes, I've found the log entry
r42123 | ihaka | 2007-07-05 02:00:05 +0200 (Thu, 05 Jul 2007) | 4 lines
Changed the behaviour of out-of-bounds negative
subscripts to match that of S. Such values are
now ignored rather than tripping an error.
So, it was changed on purpose, by one of the true Rs, very
much on purpose.
Making it a *warning* instead of the original error
may have been both more cautious and more helpful for
detecting programming errors.
OTOH, John Chambers, the father of S and hence grandfather of R,
may have had good reasons why it seemed more logical to silently
ignore such out of bound negative indices:
One could argue that
x[-5] means leave away the 5-th element of x
and if there is no 5-th element of x, leaving it away should be a
no-op.
After all this musing and history detection, my gut decision
would be to only change the documentation which Ross forgot to change.
But of course, it may be interesting
Re: [Rd] Shouldn't vector indexing with negative out-of-range index give an error?
Hi,
On 05/06/2015 09:04 AM, Henrik Bengtsson wrote:
On Wed, May 6, 2015 at 1:33 AM, Martin Maechler
maech...@lynne.stat.math.ethz.ch wrote:
John Chambers j...@stat.stanford.edu
on Tue, 5 May 2015 08:39:46 -0700 writes:
When someone suggests that we might have had a reason for some peculiarity in
the original S, my usual reaction is Or else we never thought of the problem.
In this case, however, there is a relevant statement in the 1988 blue book. In
the discussion of subscripting (p 358) the definition for negative i says: the indices consist
of the elements of seq(along=x) that do not match any elements in -i.
Suggesting that no bounds checking on -i takes place.
John
Indeed!
Thanks a lot John, for the perspective and clarification!
I'm committing a patch to the documentation now.
Thank you both and also credits to Dongcan Jiang for pointing out to
me that errors were indeed not generated in this case.
I agree with the decision. It's interesting to notice that now the
only way an error is generated is when index-vector subsetting is done
using mixed positive and negative indices, e.g. x[c(-1,1)].
This is why in situations where I need to extract a single element from
an atomic vector I use [[ instead of [. It's safer (performs
bound-checking), a little bit faster (at least last time I checked), and
drops the name of the element.
BTW did you know that one can use a negative index with [[ on a
vector of length 2?
c(a=2, b=6)[[-1]]
[1] 6
c(a=2, b=6)[[-2]]
[1] 2
list(a=22, b=6:5)[[-1]]
[1] 6 5
list(a=22, b=6:5)[[-2]]
[1] 22
list(a=22, b=6:5)[[c(-1, -2)]]
[1] 6
list(a=22, b=6:5)[[c(-1, -1)]]
Also works with [[-:
x - list(a=22, b=6:5)
x[[c(-1, -2)]] - 99L
x
$a
[1] 22
$b
[1] 99 5
Not that I ever needed that feature though...
Cheers,
H.
/Henrik
Martin
On May 5, 2015, at 7:01 AM, Martin Maechler
maech...@lynne.stat.math.ethz.ch wrote:
Henrik Bengtsson henrik.bengts...@ucsf.edu
on Mon, 4 May 2015 12:20:44 -0700 writes:
In Section 'Indexing by vectors' of 'R Language Definition'
(http://cran.r-project.org/doc/manuals/r-release/R-lang.html#Indexing-by-vectors)
it says:
Integer. All elements of i must have the same sign. If they are
positive, the elements of x with those index numbers are selected. If
i contains negative elements, all elements except those indicated are
selected.
If i is positive and exceeds length(x) then the corresponding
selection is NA. A negative out of bounds value for i causes an error.
A special case is the zero index, which has null effects: x[0] is an
empty vector and otherwise including zeros among positive or negative
indices has the same effect as if they were omitted.
However, that A negative out of bounds value for i causes an error
in the second paragraph does not seem to apply. Instead, R silently
ignore negative indices that are out of range. For example:
x - 1:4
x[-9L]
[1] 1 2 3 4
x[-c(1:9)]
integer(0)
x[-c(3:9)]
[1] 1 2
y - as.list(1:4)
y[-c(1:9)]
list()
Is the observed non-error the correct behavior and therefore the
documentation is incorrect, or is it vice verse? (...or is it me
missing something)
I get the above on R devel, R 3.2.0, and as far back as R 2.11.0
(haven't check earlier versions).
Thank you, Henrik!
I've checked further back: The change happened between R 2.5.1 and R
2.6.0.
The previous behavior was
(1:3)[-(3:5)]
Error: subscript out of bounds
If you start reading NEWS.2, you see a *lot* of new features
(and bug fixes) in the 2.6.0 news, but from my browsing, none of
them mentioned the new behavior as feature.
Let's -- for a moment -- declare it a bug in the code, i.e., not
in the documentation:
- As 2.6.0 happened quite a while ago (Oct. 2007),
we could wonder how much R code will break if we fix the bug.
- Is the R package authors' community willing to do the necessary
cleanup in their packages ?
Now, after reading the source code for a while, and looking at
the changes, I've found the log entry
r42123 | ihaka | 2007-07-05 02:00:05 +0200 (Thu, 05 Jul 2007) | 4 lines
Changed the behaviour of out-of-bounds negative
subscripts to match that of S. Such values are
now ignored rather than tripping an error.
So, it was changed on purpose, by one of the true Rs, very
Re: [Rd] Shouldn't vector indexing with negative out-of-range index give an error?
Henrik Bengtsson henrik.bengts...@ucsf.edu
on Mon, 4 May 2015 12:20:44 -0700 writes:
In Section 'Indexing by vectors' of 'R Language Definition'
(http://cran.r-project.org/doc/manuals/r-release/R-lang.html#Indexing-by-vectors)
it says:
Integer. All elements of i must have the same sign. If they are
positive, the elements of x with those index numbers are selected. If
i contains negative elements, all elements except those indicated are
selected.
If i is positive and exceeds length(x) then the corresponding
selection is NA. A negative out of bounds value for i causes an error.
A special case is the zero index, which has null effects: x[0] is an
empty vector and otherwise including zeros among positive or negative
indices has the same effect as if they were omitted.
However, that A negative out of bounds value for i causes an error
in the second paragraph does not seem to apply. Instead, R silently
ignore negative indices that are out of range. For example:
x - 1:4
x[-9L]
[1] 1 2 3 4
x[-c(1:9)]
integer(0)
x[-c(3:9)]
[1] 1 2
y - as.list(1:4)
y[-c(1:9)]
list()
Is the observed non-error the correct behavior and therefore the
documentation is incorrect, or is it vice verse? (...or is it me
missing something)
I get the above on R devel, R 3.2.0, and as far back as R 2.11.0
(haven't check earlier versions).
Thank you, Henrik!
I've checked further back: The change happened between R 2.5.1 and R 2.6.0.
The previous behavior was
(1:3)[-(3:5)]
Error: subscript out of bounds
If you start reading NEWS.2, you see a *lot* of new features
(and bug fixes) in the 2.6.0 news, but from my browsing, none of
them mentioned the new behavior as feature.
Let's -- for a moment -- declare it a bug in the code, i.e., not
in the documentation:
- As 2.6.0 happened quite a while ago (Oct. 2007),
we could wonder how much R code will break if we fix the bug.
- Is the R package authors' community willing to do the necessary
cleanup in their packages ?
Now, after reading the source code for a while, and looking at
the changes, I've found the log entry
r42123 | ihaka | 2007-07-05 02:00:05 +0200 (Thu, 05 Jul 2007) | 4 lines
Changed the behaviour of out-of-bounds negative
subscripts to match that of S. Such values are
now ignored rather than tripping an error.
So, it was changed on purpose, by one of the true Rs, very
much on purpose.
Making it a *warning* instead of the original error
may have been both more cautious and more helpful for
detecting programming errors.
OTOH, John Chambers, the father of S and hence grandfather of R,
may have had good reasons why it seemed more logical to silently
ignore such out of bound negative indices:
One could argue that
x[-5] means leave away the 5-th element of x
and if there is no 5-th element of x, leaving it away should be a no-op.
After all this musing and history detection, my gut decision
would be to only change the documentation which Ross forgot to change.
But of course, it may be interesting to hear other programmeR's feedback on
this.
Martin
__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] Shouldn't vector indexing with negative out-of-range index give an error?
When someone suggests that we might have had a reason for some peculiarity in
the original S, my usual reaction is Or else we never thought of the problem.
In this case, however, there is a relevant statement in the 1988 blue book.
In the discussion of subscripting (p 358) the definition for negative i says:
the indices consist of the elements of seq(along=x) that do not match any
elements in -i.
Suggesting that no bounds checking on -i takes place.
John
On May 5, 2015, at 7:01 AM, Martin Maechler maech...@lynne.stat.math.ethz.ch
wrote:
Henrik Bengtsson henrik.bengts...@ucsf.edu
on Mon, 4 May 2015 12:20:44 -0700 writes:
In Section 'Indexing by vectors' of 'R Language Definition'
(http://cran.r-project.org/doc/manuals/r-release/R-lang.html#Indexing-by-vectors)
it says:
Integer. All elements of i must have the same sign. If they are
positive, the elements of x with those index numbers are selected. If
i contains negative elements, all elements except those indicated are
selected.
If i is positive and exceeds length(x) then the corresponding
selection is NA. A negative out of bounds value for i causes an error.
A special case is the zero index, which has null effects: x[0] is an
empty vector and otherwise including zeros among positive or negative
indices has the same effect as if they were omitted.
However, that A negative out of bounds value for i causes an error
in the second paragraph does not seem to apply. Instead, R silently
ignore negative indices that are out of range. For example:
x - 1:4
x[-9L]
[1] 1 2 3 4
x[-c(1:9)]
integer(0)
x[-c(3:9)]
[1] 1 2
y - as.list(1:4)
y[-c(1:9)]
list()
Is the observed non-error the correct behavior and therefore the
documentation is incorrect, or is it vice verse? (...or is it me
missing something)
I get the above on R devel, R 3.2.0, and as far back as R 2.11.0
(haven't check earlier versions).
Thank you, Henrik!
I've checked further back: The change happened between R 2.5.1 and R 2.6.0.
The previous behavior was
(1:3)[-(3:5)]
Error: subscript out of bounds
If you start reading NEWS.2, you see a *lot* of new features
(and bug fixes) in the 2.6.0 news, but from my browsing, none of
them mentioned the new behavior as feature.
Let's -- for a moment -- declare it a bug in the code, i.e., not
in the documentation:
- As 2.6.0 happened quite a while ago (Oct. 2007),
we could wonder how much R code will break if we fix the bug.
- Is the R package authors' community willing to do the necessary
cleanup in their packages ?
Now, after reading the source code for a while, and looking at
the changes, I've found the log entry
r42123 | ihaka | 2007-07-05 02:00:05 +0200 (Thu, 05 Jul 2007) | 4 lines
Changed the behaviour of out-of-bounds negative
subscripts to match that of S. Such values are
now ignored rather than tripping an error.
So, it was changed on purpose, by one of the true Rs, very
much on purpose.
Making it a *warning* instead of the original error
may have been both more cautious and more helpful for
detecting programming errors.
OTOH, John Chambers, the father of S and hence grandfather of R,
may have had good reasons why it seemed more logical to silently
ignore such out of bound negative indices:
One could argue that
x[-5] means leave away the 5-th element of x
and if there is no 5-th element of x, leaving it away should be a no-op.
After all this musing and history detection, my gut decision
would be to only change the documentation which Ross forgot to change.
But of course, it may be interesting to hear other programmeR's feedback on
this.
Martin
__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
